1. Field of the Invention
The present invention relates to a printer such as a thermal printer for printing a bar code or the like onto label paper.
2. Discussion of the Background
There is known a conventional printer wherein a printer body is divided into a lower unit and an upper unit, and a paper path for the conveyance of paper is formed between the lower unit and the upper unit. In the printer of such a structure, for example, the upper unit moves pivotably relative to the lower unit, centered on a pivot member disposed behind the printer body. Therefore, by attaching a print head and so on to the upper unit and a platen to the lower unit, the paper path can be opened when the upper unit is opened. In the case where a paper holder is provided in the lower unit, a roll of paper can be set easily to the paper holder by opening the paper path.
In the case of a label printer, it is necessary to provide a sensor for detecting a printing start position of label paper. If the sensor is a transmission type sensor, in which a light emitting portion and a light receiving portion are made face to face with each other via the paper path, it is necessary to pass paper between the light emitting portion and the light receiving portion. Therefore, if the label printer has the foregoing vertically divided structure able to open the paper path by opening the upper unit, it is necessary to insert paper into the gap between the light emitting portion and the light receiving portion at the time of setting paper. This paper inserting work is troublesome.
Heretofore, for facilitating the paper setting work, there has been proposed a printer wherein a transmission type sensor is made up of two sensor units capable of being opened and closed. One of a light emitting element and a light receiving element is attached to one sensor unit, while the other is attached to the other sensor unit. Therefore, at the time of setting paper, the paper path is opened by opening one sensor unit with respect to the other sensor unit. The printer having a transmission type sensor of such a structure is described for example in Japanese laid-open Patent Publication No. Hei 11 (1999)-199097.
However, in the case of a printer having the aforesaid structure of opening and closing two sensor units, it is necessary that the paper path be opened by pivoting the upper unit and one sensor unit, then after the setting of paper, the paper path be closed by pivoting the upper unit and one sensor unit, and the printer be restored to its usable state. At this time, there is a possibility that the upper unit may be closed while allowing the sensor unit to remain open, causing damage to the sensor unit.
Accordingly, an object of the present invention is to prevent damage of a sensor unit caused by forgetting to close the sensor unit at the time of closing an open upper unit, while adopting a structure able to open a paper path by pivoting one sensor unit.